Hot Corrosion Behaviour of Nickel Chromium Coating at Different Temperatures (800 °C and 900 °C) on SA213 T91 Boiler Steel Weldments

Hot corrosion is a serious problem in power generation equipment, gas turbines for ships aircrafts, energy conversion and chemical process systems. During combustion stage in heat engines, particularly in gas turbines, sodium and sulphur impurities present either in fuel or in combustion air, react to form sodium sulphate (Na₂SO₄). If the concentration of the sulphate exceeds the saturation vapour pressure at the operating metal temperature for turbine blades and vanes (700 °C-1100 °C), then deposition of the Na₂SO₄ will occur on the surface of these components. At higher temperatures the deposits of Na₂SO₄ are molten (melting point =884 °C) and can cause accelerating attack on high alloy or Cr-Mo steels. No alloy is immune to hot corrosion attack indefinitely, although there are some alloy compositions that require a long initiation time at which the hot corrosion process moves from the initiation stage to the propagation stage. Nickel-based coatings have been reported to be widely used as they combine several advantages such as abrasion, erosion and resistance to high-temperature corrosive atmospheres. In this report a comparison on the experimental performance of nickel-based coatings has been made to understand their hot corrosion mechanism.